Awk use

awk usage
Commands for text processing ; Easy to intercept content ; Support decimal operations

working principle （ And sed distinguish ）
sed equally , Are read line by line 、 Handle ; sed Is a whole line of processing ,awk Is to split a row into fields for processing

Complete grammar
awk 'BEGIN{commands}pattern{commands}END{commands}'file BEGIN Execute the command before data

pattern Commands that are executed on each line
END Execute the command after the data
example : With : Separator , lookup passwd In file bash ending , Type the first field and the seventh field

[[email protected] 1-28]# cat passwd | awk -F: 'BEGIN{print "--start--"} /bash$/{print $1,$7}END{print "--end--"} '
--start--
root /bin/bash
yalin /bin/bash
califeng /bin/bash
cali123 /bin/bash
zhaoliying /bin/bash
woshi1 /bin/bash
woshi2 /bin/bash
--end--

Statistics passwd File lines

[[email protected] 1-28]# cat passwd | awk -F: 'BEGIN{i=0} {i++} END{print i}'

Basic usage
awk -F Separator ‘/ Pattern /{ action }’ file ; The default delimiter is blank ( Space or tab key )
awk Instructions must be enclosed in single quotation marks , Make sure you use curly braces {} Cover up
Patterns are regular expressions , Use / delimiter
Use... Between multiple actions ; Separate
Examples of basic commands
As long as the mode has no action result and grep similar , Show $0

	[[email protected] 1-28]# awk '/bash/' passwd 
	root:x:0:0:root:/root:/bin/bash
	yalin:x:1009:1009::/home/yalin:/bin/bash
	califeng:x:1010:1010::/home/califeng:/bin/bash
	cali123:x:1011:1011::/home/cali123:/bin/bash
	zhaoliying:x:1012:1012::/home/zhaoliying:/bin/bash
	woshi1:x:1013:1013::/home/woshi1:/bin/bash
	woshi2:x:1014:1014::/home/woshi2:/bin/bash

Interception function

	[[email protected] 1-28]# who | awk '{print $2}'
	tty1
	pts/0

Realize string splicing , The custom string needs to be ""

[[email protected] 1-28]# who | awk '{print "time:"$4,$2}'
	time:10:29 tty1
	time:10:29 pts/0

~ Fuzzy matching == Exactly match ！ Mismatch

[[email protected] 1-28]# who | awk '$2~"tt" {print $0}'
root     tty1         2021-01-28 10:29
[[email protected] 1-28]# who | awk '$2=="tty1" {print $0}'
root     tty1         2021-01-28 10:29
[[email protected] 1-28]# who | awk '$2!="tty1" {print $0}'
root     pts/0        2021-01-28 10:29 (192.168.0.123)

Used in conjunction with defining symbols \b Don't recognize Only use <>

[[email protected] 1-28]# cat passwd | awk -F: '$1 ~ /\<....\>/ {print $1}'
root
sync
halt
mail
dbus
sssd
sshd
rngd

awk Built-in variables
NR Represents the currently processed line number number of record
NF Number of fields representing a row number of field
FS Current input delimiter , The default is blank （ Space and tab）
FNR Number of records read from the file （ Line number ）, from 1 Start
OFS Current output separator , Default is space
example ： Output who The first, second, and last fields in , And use - Connect

[[email protected] 1-28]# who | awk 'OFS="-"{print $1,$2,$NF}'
root-tty1-10:29
root-pts/0-(192.168.0.123)

awk Built in functions
int（x） return x Truncated to the value of an integer

[[email protected] 1-9]# awk 'BEGIN {a=6.1572;result=int(a);print result}'
6

rand()
Return any number n（0<=n<1）

[[email protected] 1-9]# awk 'BEGIN {print rand()}'
0.924046
[[email protected]lhost 1-9]# awk 'BEGIN {print rand()}'
0.924046
 No random seed is set , The random numbers are the same 

srand()
Often with rand() Used together to produce random values
srand() It needs to be written in BEGIN modular , To generate random numbers normally , This is a awk The working mechanism of

[[email protected] 1-9]# awk 'BEGIN {srand();print rand()}'
0.501409
[[email protected] 1-9]# awk 'BEGIN {srand();print rand()}'
0.0852438

sub( Old string , New string , character string )
The third string is optional , The default is $0

[[email protected] 1-9]# awk 'BEGIN{ str="Hello World!";print "Before:" str;sub("World","Jack",str);print "After:" str }'
Before:Hello World!
After:Hello Jack!

index( character string 1, character string 2)
In string 1 Find string in 2, from 1 Numbered starting , Get a string 2 Value ; If not found, return 0

[[email protected] 1-9]# awk 'BEGIN{ str="AA BB CC";subs="BB";ret=index(str,sub);printf ret}'
4

ength（ character string ）
Returns the length of the string

[[email protected] 1-9]# awk 'BEGIN {str="hello!!I am Anna!";print length(str)}' 
17

split( character string , Array , Separator )
Divide the string into array elements according to the separator and store them in the array

[[email protected] 1-9]# awk 'BEGIN {str="AA,BB,CC,DD,EE";split(str,arr,",");for(i in arr){ print arr[i]}}'
AA
BB
CC
DD
EE

system
Get the command return value ;0 Indicates that the last command was executed successfully ; Not 0 Indicates that the last command failed to execute

[[email protected] 1-9]# awk 'BEGIN { ret=system("date");print ret}'
2021 year  01 month  09 Japan   Saturday  20:48:17 CST
0

awk quote shell Variable
-v quote shell Variable （ When there are fewer variables ）

[[email protected] 1-9]# name="lisi"
[[email protected] 1-9]# echo | awk -v abc=$name '{print abc}'
lisi

Use double quotation marks, single quotation marks and $takechangeThe\; amountenclosedriseCome\; on;alongorderyes：doubleleadNumbersingleleadNumber$ Single quotation mark and double quotation mark

[[email protected] 1-9]# awk 'BEGIN{print "'$name'"}'
lisi

Use double quotes ,awk Inside $0、$n And so on

[[email protected] 1-9]# abc=zhaoliying
[[email protected] 1-9]# awk -F: "/^$abc/{print NR,\$0} " /etc/passwd
29 zhaoliying:x:1012:1012::/home/zhaoliying:/bin/bash
[[email protected] 1-9]# awk -F: "/^$abc/{print \$1,\$3} " /etc/passwd
zhaoliying 1012

Use single quotes , Splicing parameter transfer

sg=3
[[email protected] ~]# awk -F: '/root/{print $1,$'$sg'}' /etc/passwd
root 0
operator 11
-------------------------------------------------------------------
[[email protected] ~]#awk -F: "/root/{print \$1,\$sg}" /etc/passwd
root root:x:0:0:root:/root:/bin/bash
operator operator:x:11:0:operator:/root:/sbin/nologin

practice
View users who have not set a password （ The second field is * perhaps ！！ Not set ）
cat shadow | awk -F: ‘BEGIN{i=0} {length($2)<=2;i++;print $1" No password set "} END{print “ Yes "i" No password is set ”}’
Use NF Variable display passwd The contents of the penultimate column of the document
cat passwd | awk -F’[: /]’ ‘{print $(NF-1)}’
Show passwd Document No. 5 To the first 10 The user name of the line
cat passwd | awk -F: ‘{print $1}’ | sed -n ‘5p;10p’
cat passwd | awk -F: ‘NR ~/<[5-9]|10>/ {print KaTeX parse error: Expected 'EOF', got '}' at position 2: 1}̲’ Show passwd Line number in file …/ {print NR,KaTeX parse error: Expected 'EOF', got '}' at position 2: 1}̲’ passwd use ip ad…NF ~/ens33/{print $2}’ | awk -F/ ‘{print $1}’
First use ifconfig, Use awk Show eth0 Inbound and outbound traffic ( byte )
ifconfig |head -8 | awk ‘$1 ~/RX/ && $4 ~ /bytes/ || $1 ~ /TX/ && $4 ~ /bytes/ {print $0}’
ifconfig | head -8 | awk ‘$0 ~ /RX.*bytes|TX.*bytes/ {print $5}’
Use awk Command statistics are based on r Number of users at the beginning , The results are as follows
cat passwd | awk -F: ‘BEGIN{i=0} $1 ~ /^r/ {print $1;i++} END {print i};’
Show passwd Document No. 7 Column is not bash Username
cat passwd | awk -F: ‘KaTeX parse error: Undefined control sequence: < at position 7: 7 !~ /\̲<̲bash>/{print $1}’